The invention relates to an electrode-less low-pressure discharge lamp with a hermetically sealed lamp bulb, wherein a plasma is formed by creating a high-frequency electromagnetic field in the bulb interior, and radiation produced by the plasma exits from the bulb along an established optical axis through at least one body transparent to UV radiation, in a first end of the bulb, at least one diaphragm or diaphragm body with a through-bore being provided along the optical axis (10).
The lamps referred to herein as electrode-less discharge lamps are those which have no actual electrodes inside of their envelope, and in which a plasma is formed by producing an electromagnetic field; the field can be produced for example, in a capacitive manner by electrodes applied to the lamp""s envelope or bulb. It is also possible, however, to perform an inductive creation of the electromagnetic field.
DE-OS 41 20 730 discloses an electrode-less low-pressure discharge lamp in whose bulb a plasma is formed by producing a high-frequency electromagnetic field and light produced by the plasma issues from the bulb; in this case a diaphragm of a high-melting material is disposed in the area of the plasma and contains an opening for constricting the plasma area, the diaphragm having an optical axis through the opening, along which the light emerges. In order to achieve sufficiently high luminous fluxes and densities in the constriction of the high-frequency field, the materials must withstand severe wall stresses so that they do not degrade, melt, release impurities, much less shatter as a result of thermal shock when turned on and off.
According to DE-OS 41 20 730, boron nitride is preferred as the material for the diaphragm.
Furthermore, GB Patent 1,003,873 discloses an electrode-less high-frequency discharge spectral lamp which contains a sealed light bulb of transparent material, wherein the lamp bulb is divided into two parts which are joined together by a capillary tunnel, and wherein electromagnetic systems are provided for the production of a discharge within the metal vapor in the bulb. The injection of the electromagnetic energy for the discharge is sustained by a coil system surrounding the lamp bulb, the actual ignition being performed through external electrodes.
Great problems regarding ignition were encountered according to the British patent, so that additional electrodes had to be provided outside of the lamp bulb to initiate ignition; radiation directed along a preferred beam axis is not provided therein.
Furthermore, DE 195 47 519 A1 has disclosed an electrode-less low-pressure discharge lamp, especially a deuterium lamp, which has a cylindrically symmetrical diaphragm which contains a cavity at each of its ends; the two cavities are connected together by a bore which simultaneously serves as the diaphragm aperture for the purpose of constricting the plasma produced by creating a high-frequency electromagnetic field in the interior to increase the intensity of the light emitted. Both ends of the cylindrically symmetrical diaphragms are provided with a hermetic seal, at least one of which is configured as an exit window; in a preferred embodiment the creation of the electromagnetic field is accomplished capacitively by electrodes located on the end surfaces which have at least one opening for the emission of the radiation provided that they are adjacent to an exit window.
DE 195 47 813 C2 likewise discloses an electrode discharge lamp with diaphragm. In the discharge vessel a plasma is formed by producing a high-frequency electromagnetic field and through it the light produced by the plasma issues from the discharge vessel through an area of the discharge vessel that is transparent at least to UV light, at least one diaphragm of high-melting material being arranged in the area of the plasma and having at least one opening for the constriction of the plasma area. In the plasma area at least two diaphragm apertures are provided on an optical axis along which the light issues, the discharge vessel being provided along the beam axis at each of its ends with a broad electrode for the capacitive production of the electromagnetic field; at the same time at least one of the electrodes contains an opening in the area of the axis of the beam exit, which is arranged adjacent to an exit window permeable to ultraviolet light.
The known discharge lamps have proven problematical in regard to complete UV/vis light sources for analytic purposes, wherein a lamp unit has a deuterium lamp and a tungsten lamp in a shine-through arrangement which together with a shutter contains an SMA optical waveguide terminal and an input apparatus for both lamps on a printed circuit board. In systems with additional condenser lenses, transmission losses occur upon exit from a window transparent to ultraviolet and upon passing through the condenser lens.
The invention is addressed to the problem of offering a very simple and hand-held light source which has low transmission losses and is suitable for board construction in a miniature size. Furthermore, it must be possible in a comparatively simple manner to inject the light into a light-conducting fiber.
The problem is solved by the fact that the transparent body is formed as a lens in the first end of the lamp bulb.
It proves to be advantageous that the transmission of the ultraviolet light is considerably improved; thus one material penetration is eliminated, since instead of the former penetration of the radiation through window and lens only a single penetration of the radiation through lens material is necessary. The result is not only simplified construction but also an improved yield of light.
Advantageous embodiments of the invention according to claim 1 are given in claims 2 to 13.
In one preferred embodiment, at least one lens is made as a body transparent to ultraviolet radiation. Along the optical axis an additional transparent body is disposed in the area of a second end of the bulb, the transparent bodies forming at their bulb ends a hermetically tight junction in their marginal area.
For the capacitive generation of the electromagnetic field, the lamp bulb is provided along its axis with a broad electrode at each of its ends, each of the electrodes containing an opening in the area of the axis of the beam""s exit which is disposed adjacent to the exit.
In a preferred embodiment, an additional radiation source in the form of a thermal radiator is disposed along the optical axis in the area of the second end outside of the lamp bulb, whose radiation enters the bulb through the transparent body of the second end, both the radiation produced by the plasma and the radiation of the thermal radiator being carried out through the transparent body of the first end.
The thermal radiator is arranged along the beam axis, the radiation of the thermal radiator being guided by the diaphragm aperture at the beam exit; this means that both the radiation produced by the plasma and the radiation of the thermal radiator are guided by the first transparent body configured as an ultraviolet-permeable lens.
The diaphragm aperture of the beam exit is of circular configuration, its diameter ranging from 0.1 to 6 mm; the diaphragm consists preferably of aluminum oxide, aluminum nitride, or boron nitride; it can also consist, however, of thorium oxide, beryllium oxide, polycrystalline diamond or a high-melting metal such as molybdenum or tungsten.
The ultraviolet-permeable lens and the window of the beam inlet consist preferably of quartz glass, glass transparent to ultraviolet, or sapphire.
Preferably deuterium is used to fill the lamp bulb with a cold fill pressure of 1 to 100 mbar. The electrodes are connected to a high-frequency generator which produces an excitation frequency ranging from 0.1 KHz to 2450 MHz.
Furthermore, savings of material and manufacturing costs are advantageously obtained due to the fact that now an exit window serving also as a condenser lens is used, and also the calibration operation for a proper mounting and positioning of the lens at a certain distance from the lamp is eliminated.
Another advantage is to be seen is the coverage of a wider angle by the emitted light since the lens is brought closer to the radiating plasma spheres in the area of the diaphragm. This too results in an elevated light yield.
Furthermore, the space formerly between the discharge lamp and condenser lens can now be used for a greater volume of gas in the discharge lamp, so that a longer useful life of the discharge lamp can be achieved, requiring the same amount of space.